It is common practice in packaging many goods, including food items and particularly, meat products, to use a substantially rigid tray and a flexible, polymeric upper lid. During the packaging process, the product is placed in the tray. The lidding material is fed from a roll across the tray, covers the product, and typically is sealed to the tray edges to form the finished package. However, relatively bulky or awkwardly shaped products which extend above the upper flange of a conventional packaging tray, i.e., high profile products, are not readily accommodated by such a packaging operation.
High profile meat products are regularly packaged in supermarkets in an in-store overwrap process. By such process, the high profile product is placed in a tray, a polymeric film is stretched around the product and tray, and then the overwrapped tray is pressed onto a heated plate to weld together the pleats and folds of the film at the underside of the tray. The resultant package, an upper film tensioned across the uppermost portions of the high profile product and extending, under tension, to the outer edges of the tray, is readily recognized by consumers. Yet, the preparation of such packages on an individual basis has long been recognized to be inefficient and expensive. Instead, it is preferable to butcher and package such meat products at a central processing facility which benefits from economies of scale, and then ship the packaged meat to individual supermarkets or other retail outlets. It is believed that the central processing of meat can also lead to a higher quality, more sanitary product with a longer shelf-life than meat which is butchered and packaged in individual supermarkets.
One method for providing centrally packaged high profile meat products has been vacuum skin packaging (VSP). In a typical vacuum skin packaging process, the product is placed on a support member, a thermoformable film is extended over product and support member, the film is drawn upwardly into a cavity above the product and heated to its softening temperature, the space between the upwardly drawn film and the product and support member is evacuated and the heated film is released onto the product, thermoforming itself to the product and welding to the remaining upper surface area of the support member.
Vacuum skin packaging is an excellent packaging process for a variety of products.
However, there are some drawbacks to vacuum skin packaging high profile products. First, it can be difficult to provide an upper VSP film which is capable of being sufficiently drawn to accommodate an irregularly shaped high profile product without undue thinning and potential breakage in the crevices of the product or without unsightly folds and pleats in the film where it welds to the support member. Second, even a perfectly vacuum skin packaged high profile product can present an unusual and, therefore, less preferred appearance to consumers who are accustomed to the appearance of in-store overwrapped packages.
The concerns with packaging a high profile product are exacerbated when the product is one, as is the case for many meat products, which must be packaged under certain environmental conditions. For example, for some meat products it is desirable to package and distribute the meat in a low oxygen environment and then expose the meat to a high oxygen environment immediately prior to presentation for sale. For such meat products a substantially gas-impermeable lidding film which peelably delaminates (i.e., delaminates upon peeling) to expose a gas-permeable film, thereby causing a change in the environmental conditions within the package is often employed.
As is discussed above, historically, large sub-primal cuts of meat have been butchered and packaged in each supermarket. Fresh red meat presents a particular challenge to the concept of centralized processing and packaging due to its oxygen-sensitivity. Such oxygen-sensitivity is manifested in the shelf-life and appearance (color) of a packaged meat product. For example, while a low-oxygen packaging environment generally increases the shelf-life of a packaged meat product (relative to meat products packaged in an environment having a higher oxygen content), red meat has a tendency to assume a dark red color when packaged in the absence of oxygen or in an environment having a very low oxygen concentration, i.e., below about 5% oxygen. Unfortunately, such a dark red color is undesirable to most consumers, and marketing efforts to teach the consumer about the acceptability of the dark red color have been largely ineffective. When meat is exposed to a sufficiently high concentration of oxygen, e.g., as found in air, it assumes a bright red color which most consumers associate with freshness. After 1 to 3 days of such exposure, however, meat assumes a brown color which, like. the dark red color, is undesirable to most consumers (and indicates that the meat is beginning to spoil).
Thus, in order to effectively butcher and package meat products in a central facility for distribution to retail outlets, the meat would desirably be packaged, shipped, and stored in a low-oxygen environment for extended shelf-life, and then displayed for consumer sale in a relatively high-oxygen environment such that the meat is caused to xe2x80x9cbloomxe2x80x9d into a red color just before being placed in a retail display case. While in the retail display case, the meat product is desirably contained in a package which protects it from microbial and other contamination. In order to attain the maximum economic benefit from centralized packaging, the package in which the meat product is displayed for consumer sale is the same package in which the meat product is initially packaged and shipped from the central processing facility.
Accordingly, there is a need in the art for a package and process for centrally packaging high profile products which provides a conventional package appearance and which may be employed for environment-sensitive products.
Such need is met by a packaging process which includes the steps of providing a support member which includes a product support surface and a periphery, providing an upper film which includes a sealant layer, the sealant layer being sealable to the support member, orienting the film to an orientation ratio of from about 9.0:1 to about 16.0:1, positioning a product on the product support surface of the support member such that at least a portion of the product extends upwardly above the level of the periphery, extending the upper film above the support member and product, the sealant layer being immediately above and adjacent to the support member and the product, drawing the upper film into a concavity by differential pressure, maintaining the concave shape of the upper film while heating the film, removing gases from the space between the upper film and the support member and product, introducing a desirable gas into the space, releasing the upper film such that it shrinks toward the product and the support member, the desirable gas being retained within the space precluding close contact of the film with the lowermost portions of the product, and sealing the upper film to the periphery of the support member, wherein at least the step of heating the film shrinks the film, thereby tensioning it onto and across the underlying product.
This need is also met by providing a package which includes a support member which includes a product support surface and a periphery, a product contained on the product support surface, at least a portion of the product extending upwardly above the level of the periphery, an oriented upper film tensioned across and at least partially heat shrunk onto the uppermost portions of the product and sealed to the periphery of the support member, and a desired gas trapped between the support member and the upper film.
As used herein, the term xe2x80x9cfilmxe2x80x9d refers to a thermoplastic material, generally in sheet or web form, having one or more layers formed from polymeric or other materials. A film can be a monolayer film (having only one layer) or a multilayer film (having two or more layers).
As used herein, the term xe2x80x9cmultilayerxe2x80x9d refers to film comprising two or more layers which are bonded together by one or more of the following methods: coextrusion, extrusion coating, vapor deposition coating, solvent coating, emulsion coating, or suspension coating.
As used herein, the terms xe2x80x9cextrusion,xe2x80x9d xe2x80x9cextrude,xe2x80x9d and the like refer to the process of forming continuous shapes by forcing a molten plastic material through a die, followed by cooling or chemical hardening. Immediately prior to extrusion through the die, the relatively high-viscosity polymeric material is fed into a rotating screw, which forces it through the die.
As used herein, the term xe2x80x9ccoextrusion,xe2x80x9d xe2x80x9ccoextrude,xe2x80x9d and the like refer to the process of extruding two or more materials through a single die with two or more orifices arranged so that the extrudates merge and weld together into a laminar structure before chilling, i.e., quenching. Coextrusion can be employed in film blowing, free film extrusion, and extrusion coating processes.
As used herein, the term xe2x80x9clayerxe2x80x9d refers to a discrete film component which is coextensive with the film and has a substantially uniform composition. In a monolayer film, tile xe2x80x9cfilmxe2x80x9d and xe2x80x9clayerxe2x80x9d would be one and the same.
As used herein, the terms xe2x80x9cdelaminate,xe2x80x9d xe2x80x9cdelaminates,xe2x80x9d and the like refer generally to the internal separation of a film or laminate and, more specifically, to the separation of a coextruded, multilayer film within a layer and/or at an inter-layer (i.e., layer/layer) interface within the coextruded film when such film, or laminate of which the coextruded film is a component, is subjected to a peel force of sufficient magnitude.
As used herein, the term xe2x80x9cintra-film cohesive strengthxe2x80x9d refers to the internal force with which a film remains intact, as measured in a direction that is perpendicular to the plane of the film. In a multilayer film, intra-film cohesive strength is provided both by inter-layer adhesion (the adhesive strength between the layers which binds them to one another) and by the intra-layer cohesion of each film layer (i.e., the cohesive strength of each of the film layers). In a monolayer film, intra-film cohesive strength is provided only by the intra-layer cohesion of the layer which constitutes the film.
As used herein, the terms xe2x80x9cpeel,xe2x80x9d xe2x80x9cpeeling,xe2x80x9d and the like refer generally to the act of removing one or more layers from a multilayer film by manually grasping and pulling back the layers along a plane or interface of relatively low bond-strength or within a layer having relatively weak intra-layer cohesion.
As used herein, the term xe2x80x9cpeel forcexe2x80x9d refers to the amount of force required to ply-separate two layers, and/or internally separate one layer, of a multilayer film or laminate, as measured in accordance with ASTM F904-91.
As used herein, the term xe2x80x9cbond-strengthxe2x80x9d refers generally to the adhesive force with which two adjacent films, or two adjacent film layers, are connected and, more specifically, to the force with which two films are connected by a heat-weld. Bond-strength can be measured by the force required to separate two films or film layers that are connected, e.g., via a heat-weld, in accordance with ASTM F88-94.
As used herein, the phrase xe2x80x9cgas-permeablexe2x80x9d refers to a film or film portion which admits at least about 1,000 cc of gas, such as oxygen, per square meter of film per 24 hour period at 1 atmosphere and at a temperature of 73xc2x0 F. (at 0% relative humidity). More preferably, a gas-permeable film or film portion admits at least 5,000, even more preferably at least 10,000, such as at least 15,000, 20,000, 25,000, 30,000, 35,000, 40,000, and 50,000, and most preferably at least 100,000 cc of oxygen per square meter per 24 hour period at 1 atmosphere and at a temperature of 73xc2x0 F. (at 0% relative humidity). In accordance with the present invention, a gas-permeable film or film portion can itself have the aforedescribed levels of gas permeability or, alternatively, can be a film or film portion which does not inherently possess the aforedescribed levels of gas permeability but which is altered, e.g., perforated or peelably delaminated, to render the film gas-permeable as defined above.
As used herein, the phrase xe2x80x9csubstantially gas-impermeablexe2x80x9d refers to a film or film portion which admits less than 1000 cc of gas, such as oxygen, per square meter of film per 24 hour period at 1 atmosphere and at a temperature of 73xc2x0 F. (at 0% relative humidity). More preferably, a substantially gas-impermeable film admits less than about 500, such as less than 300, and less than 100 cc of gas, more preferably still less than about 50 cc, and most preferably less than 25 cc, such as less than 20, less than 15, less than 10, less than 5, and less than 1 cc of gas per square meter per 24 hour period at 1 atmosphere and at a temperature of 73xc2x0 F. (at 0% relative humidity).
As used herein, the phrase xe2x80x9cproduct support memberxe2x80x9d refers to a component of a package on or in which a product is disposed. Meat products are typically disposed in a tray-like package component comprising, e.g., expanded polystyrene sheet material which has been thermoformed into a desired shape, for supporting the meat product. The support member of the present inventive package may be flat or substantially planar but is preferably formed in the shape of a tray, That is, the support member necessarily includes a product support surface for receiving and supporting the product being packaged and a periphery to which the upper film is sealed. Preferably, the support member includes a downwardly formed cavity and an upper flange, wherein the product support surface is defined by the downwardly formed cavity and wherein the upper flange is the periphery of the support member.
The support member may be semi-rigid but is preferably rigid. It may be thermoformed in-line with the packaging operation or provided preformed. Depending on the product being packaged and the ultimate end-use application the support member may be gas permeable or substantially gas impermeable. Depending on the composition of the sealant layer of the upper film and, optionally, the desired gas barrier properties of the overall package, the support member may include a sealant film.
As used herein, the phrase xe2x80x9csealant filmxe2x80x9d refers to a film which is conformably bonded to at least one of the exterior surfaces of a product support member. Preferably, the sealant film is bonded to the upper, as opposed to the lower, exterior surface of the support member and is a substantially gas-impermeable film.
xe2x80x9cOrientationxe2x80x9d involves stretching a film at an elevated temperature (the orientation temperature) followed by setting the film in the stretched configuration (e.g., by cooling). When an unrestrained, non-annealed, oriented polymeric film subsequently is heated to its orientation temperature, heat shrinkage occurs and the film returns almost to its original, i.e., pre-oriented, dimensions.
An oriented film has an xe2x80x9corientation ratioxe2x80x9d, which is the multiplication product of the extent to which the film has been expanded in several directions, usually two directions perpendicular to one another. Expansion in the longitudinal direction, sometimes referred to as the machine direction, occurs in the direction the film is formed during extrusion and/or coating. Expansion in the transverse direction means expansion across the width of the film and is perpendicular to the longitudinal direction. Thus, if a film has been oriented to three times its original size in the longitudinal direction (3:1) and three times its original size in the transverse direction (3:1), then the overall film has an orientation ratio of 3xc3x973 or 9:1.
As used herein, the term xe2x80x9cheat-sealxe2x80x9d (also known as a xe2x80x9cheat-weldxe2x80x9d) refers to the union of two films by bringing the films into contact, or at least close proximity, with one another and then applying sufficient heat and pressure to a predetermined area (or areas) of the films to cause the contacting surfaces of the films in the predetermined area to become molten and intermix with one another, thereby forming an essentially inseparable bond between the two films in the predetermined area when the heat and pressure are removed therefrom and the area is allowed to cool. In accordance with the practice of the present invention, a heat-seal preferably creates a hermetic seal, i.e., a barrier to the outside atmosphere.